Actinobacillosis (Wooden Tongue) in Sheep

Actinobacillosis is a bacterial infection of soft tissues, most often caused by Actinobacillus lignieresii. In sheep, it can affect the tongue, lips, cheeks, gums, throat area, and nearby lymphatic tissues. When the tongue becomes firm, enlarged, and painful, people often call it wooden tongue.

This bacterium is commonly associated with the mouth and upper digestive tract. Disease usually develops when rough feed, thorns, stems, or other trauma create tiny wounds that let bacteria move deeper into tissue. The body then responds by forming firm, inflamed, sometimes pus-filled granulomatous lesions.

Wooden tongue is reported much more often in cattle, but sheep can develop it too. In sheep, the biggest day-to-day problem is often reduced ability to graze, chew, and swallow. That means even a localized mouth infection can quickly turn into dehydration, weight loss, and weakness if care is delayed.

The good news is that many cases respond well when your vet identifies the problem early and starts treatment before the tongue or surrounding tissues become severely scarred or obstructive.

The usual cause is infection with Actinobacillus lignieresii, a gram-negative bacterium that can live in the mouth and forestomach environment of ruminants. It often acts as an opportunist rather than an outside invader. In other words, the bacteria may already be present, but they need damaged tissue to cause disease.

Small injuries inside the mouth are a common trigger. Coarse hay, stemmy forage, thistles, awns, brush, sharp feed particles, or other abrasive material can create tiny punctures or scrapes in the tongue and oral lining. Once bacteria enter those tissues, the body forms chronic inflammatory nodules and abscesses that make the tongue feel hard and less mobile.

Outbreaks can be linked to rough, abrasive feed sources, although many cases are isolated. Poor body condition, delayed treatment, and ongoing mouth trauma may make lesions more severe or slower to resolve. The condition is considered sporadic and is generally difficult to prevent completely.

Because several other diseases can also cause mouth swelling, drooling, or trouble eating in sheep, it is important not to assume every swollen tongue is wooden tongue. Trauma, foreign bodies, tooth-root disease, caseous lymphadenitis, bluetongue, oral abscesses, and other infections can look similar at first.

Your vet will usually start with a hands-on oral exam and a close look at how the sheep eats, chews, and swallows. A firm, painful tongue with reduced movement is a classic clue. Your vet may also check for swellings under the jaw, draining tracts, dehydration, fever, and body condition changes.

Diagnosis is often based on the history, exam findings, and the pattern of lesions. If there is discharge or tissue available, your vet may collect samples for cytology, bacterial culture, PCR, or histopathology. In confirmed cases, tissue may show granulomatous abscesses, and the organism can sometimes be identified from samples.

Additional testing can be helpful when the presentation is unusual, severe, or not responding as expected. Depending on the case, your vet may recommend ultrasound of soft tissue swellings, evaluation for foreign bodies, or testing to rule out other causes of oral disease. Bloodwork is not always diagnostic for this condition, but it may help assess dehydration or overall health in a sick sheep.

A response to treatment can support the diagnosis, but it should not replace a proper exam. In food animals, medication selection, route, and withdrawal guidance need to be handled carefully by your vet.

Prevention focuses on reducing mouth trauma and catching cases early. Check hay and forage quality when possible, especially if feed is very coarse, stemmy, thorny, or contaminated with sharp plant material. If multiple sheep develop oral pain or drooling after a feed change, contact your vet and review that feed source right away.

Good flock observation matters. Sheep often hide illness until weight loss or dehydration is already developing. Watching for slow eating, feed dropping, drooling, or jaw swelling can help your vet intervene before lesions become extensive.

Routine handling also helps. During flock checks, look at body condition, chewing behavior, and the mouth area. Remove obvious environmental hazards when practical, and work with your vet on overall flock health, since animals in poor condition may cope less well with painful oral disease.

There is no widely used vaccine for wooden tongue in sheep, and because the disease is sporadic, prevention is not always perfect. The most realistic goal is lowering oral injury risk, responding quickly to suspicious signs, and using a treatment plan that fits the sheep's needs and your operation.